Communications using circular polarized waves are commonly conducted in the fields of mobile communications and satellite communications. Helical antennas and spiral antennas capable of transmitting and receiving circular polarized waves are commonly employed in communications using these circular polarized waves.
A helical antenna has maximum directivity in the direction of its helical winding axis, while a primary mode spiral antenna has maximum directivity in a perpendicular direction to the antenna surface. A secondary mode spiral antenna has bidirectional radiation characteristics.
However, in the field of communications, there are cases where a particular communications direction is required, as in satellite communications. If a specific communications direction is required the antenna beam must be set such that it matches the angle of elevation and the azimuth angle thereof.
Therefore, conventionally, the antenna is so constructed that the angle of elevation of the antenna beam can be matched to the angle of elevation of the communications direction by inclining the antenna itself, and the antenna as a whole is rotatable so that when it is mounted in a mobile station, it can be aligned with the azimuth angle of the communications direction.
However, if the antenna itself is inclined such that the beam emitted from the antenna has a specific angle of elevation, then the surface area of the antenna exposed to wind increases and it becomes necessary to strengthen the antenna fixing means. Moreover, the height of the antenna increases and there is a risk that it may exceed a maximum height when it is mounted in a mobile station.
Therefore, it is an object of the present invention to provided a single wire spiral antenna whereby the surface area of the antenna exposed to the wind can be reduced, the height of the device can be reduced, and the radiation beam of a circular polarized wave can be tilted.